1. Field of the Invention
The present invention relates to engine starting control systems having a motor coupled with the output shaft of an engine and a transmission, and in particular, relates to systems for starting the engine by using the motor.
2. Description of the Related Art
In general, a hybrid vehicle has an engine and a motor as driving sources, a portion of the output of the engine or the kinetic energy of the vehicle is converted into electric energy, and the converted electric energy is stored in a battery system. Some hybrid vehicles have an automatic transmission and an engine starting system, and when the engine is started, the electric energy stored in the battery system is used to drive the motor, so as to perform engine cranking by using the motor.
In order to reliably start the engine in such an engine starting system, the starting torque of the motor is maintained for a specific time after the engine is started (refer to, for example, Japanese Unexamined Patent Application, First Publication No. Hei 10-331749).
In a control system for hybrid vehicles having the above-explained engine starting system, the motor torque generation time is short (e.g., approximately 1.5 sec) so as to minimize energy consumption as much as possible. This setting causes no problem when the vehicle is driven under normal conditions.
However, if the fuel is low quality gasoline or the like, the required torque may not be obtained when the set generation time has passed. In this case, when the automatic transmission is set in the in-gear state after the starting of the engine, the engine (rotation) speed may decrease or the engine may stall. In order to prevent such a situation, the motor torque generation time may be set to be longer. However, in this case, power consumption of the motor increases so that the battery system (e.g., a battery) tends to discharge, so that an energy management problem may occur or the capacity (i.e., size) of the battery system may have to be increased.
In consideration of the above circumstances, an object of the present invention is to provide a control system for hybrid vehicles, which can improve the reliability of the engine starting by using a motor and suppress energy consumption at the engine starting.
Therefore, the present invention provides an engine starting control system comprising:
a motor (e.g., a motor M in an embodiment explained below) coupled with an output shaft of an engine (e.g., an engine E in the embodiment explained below);
a transmission (e.g., an automatic transmission T in the embodiment explained below);
a motor control section (e.g., a motor ECU 1 in the embodiment explained below) for starting the engine by using the motor according to a request for starting the engine;
an in-gear detecting section for detecting an in-gear state of the transmission (refer to a CVT in-gear determination flag F_ATNP in the embodiment explained below);
a measurement section for measuring an elapsed time from the starting time of the engine operation (refer to a timer T01ACR in the embodiment explained below); and
an engine speed detecting section (e.g., an engine speed sensor S2 in the embodiment explained below) for detecting an engine speed of the engine, wherein:
the motor control section starts engine cranking using the motor according to the request for starting the engine; and
when the elapsed time measured by the measurement section reaches a first predetermined time and the in-gear detection section detects that the transmission is in the in-gear state, the motor control section continues the engine cranking if the engine speed detected by the engine speed detecting section is equal to or less than a predetermined engine speed (e.g., a self-recovery engine speed #NCRMOT in the embodiment explained below) defined for determining whether the engine reaches a predetermined starting phase.
According to the above structure, while the transmission is in the in-gear state after the engine is started, engine cranking using the motor can be continued until the engine speed exceeds the above-explained predetermined engine speed.
the engine cranking may be continued for a second predetermined time which is longer than the first predetermined time. Accordingly, the engine can be reliably started.
If the engine speed detecting section detects an engine speed equal to or greater than the predetermined engine speed during the second predetermined time, the motor control section may complete the engine starting operation using the motor. Accordingly, a necessary and minimum duration for the engine cranking using the motor can be obtained.
If the engine speed detecting section detects an engine speed equal to or greater than the predetermined engine speed after the second predetermined time has elapsed, the motor control section may complete the engine starting operation using the motor. Accordingly, it is possible to prevent the engine cranking using the motor from being continued endlessly.
Typically, the motor is a drive motor for a hybrid vehicle, wherein an output of the motor is added to the engine output. In this case, the performance of the engine starting of the hybrid vehicle can be improved.
The present invention also provides an engine starting control method (corresponding to the above system) comprising:
a motor control step of starting an engine by using a motor according to a request for starting the engine, where the motor is coupled with an output shaft of the engine;
an in-gear detecting step of detecting an in-gear state of a transmission;
a measurement step of measuring an elapsed time from the starting time of the engine operation; and
an engine speed detecting step of detecting an engine speed of the engine, wherein:
the motor control step includes starting engine cranking by using the motor according to the request for starting the engine; and
when the elapsed time measured in the measurement step reaches a first predetermined time and it is detected in the in-gear detection step that the transmission is in the in-gear state, the engine cranking performed in the motor control step is continued if the engine speed detected in the engine speed detecting step is equal to or less than a predetermined engine speed defined for determining whether the engine reaches a predetermined starting phase.